This invention relates generally to a method for controlling air/fuel ratio of a mixture supplied to an internal combustion engine by means of a feedback control system. More particularly, the present invention relates to such a method for controlling air/fuel ratio on the basis of detected concentration of an exhaust gas component.
In a typical conventional feedback air/fuel ratio control system for an internal combustion engine of an automotive vehicle or the like, the air fuel ratio of the mixture is determined by correcting a basic or standard quantity or flow rate of fuel to be supplied to the engine cylinders in accordance with various information relating to engine parameters and the concentrations of a given gas in the exhaust gasses. In the conventional feedback air/fuel ratio control systems, the quantity of fuel supplied to the engine per unit time is controlled on the basis of the integration of the output signal of the air/fuel ratio sensor. Therefore, in the transient conditions of the engine operation, if the air/fuel ratio varies at a higher speed than the correcting speed based on the integration control, the correction cannot catch up with the variation of the actual air/fuel ratio. Furthermore, in the case that the air/fuel ratio sensor is inactive, an accurate control of air/fuel ratio cannot be performed, for instance, feedback control cannot be performed, to cause the deterioration of the exhaust gasses.